Conventionally, brain perfusion analysis is known in the diagnosis of cerebral infarction with an X-ray computed tomography (CT) apparatus. In the brain perfusion analysis, there is used a brain perfusion image that is tomograms of the brain taken through injection of a contrast media and represents the state of blood perfusion.
Furthermore, in recent years, there is known an analysis method to manually or automatically set a boundary line that divides a cross-sectional image of the head taken with an X-ray CT apparatus into two parts of the right and left hemispheres, reverse one of images divided by the boundary line and superimpose the reversed image on the other image, and create a subtraction image between the superimposed images. According to this analysis method, a lesion area stands out in the subtraction image; therefore, comparative reading of the right and left hemispheres is facilitated, and this makes it possible to check abnormal blood flow such as cerebral infarction. However, the above-described conventional technology may fail to make an accurate comparison between a preoperative image and a postoperative image.